The present invention, in some embodiments thereof, relates to chemical conjugates and their use in therapy and diagnosis and, more particularly, but not exclusively, to chemical conjugates of a polymer having attached thereto an anti-angiogenesis agent and a bone targeting moiety, which are useful in the diagnosis, treatment and monitoring of bone related diseases and disorders such as bone cancer and bone metastases.
Osteosarcoma is the most common type of primary bone cancer and classified as a malignant mesenchymal neoplasm in which the tumor directly produces defective osteoid (immature bone). It is a highly vascular and extremely destructive malignancy that most commonly arises in the metaphyseal ends of long bones. Over the past two decades, multimodality treatment consisting of aggressive chemotherapy combined with radical surgical resection, has been the mainstay of osteosarcoma management, with achievable 5 year survival rates of 50 to 70% in patients who do not have metastatic disease at presentation. Several strategies were proposed, such as immune-based therapy, tumor-suppressor or suicide gene therapy, or anticancer drugs that are not commonly used in osteosarcoma. However, still one-third of patients die from this devastating type of cancer, and for those with unresectable disease there are no curative systemic therapies.
Prostate cancer is the most common cancer of males in industrialized countries and the second leading cause of male cancer mortality. Mortality in these patients is not due to primary tumor growth, but rather due to complications caused by metastases to vital organs. Prostate cancer predominantly metastasizes to bone, but other organ sites are affected including the lung, liver, and adrenal gland.
Breast cancer also often metastasizes into bones.
Bone metastases incidence in patients with advanced metastatic disease is approximately 70%. Bone metastases are associated with considerable skeletal morbidity, including severe bone pain, pathologic fracture, spinal cord or nerve root compressions, and hypercalcemia of malignancy. Chemotherapy agents, hormonal deprivation and bisphosphonates are the common treatments for advanced metastatic disease. However, with time, the disease progresses to a phase when the standard therapy fails to control the malignancy and furtherer progresses to a highly chemotherapy-resistant state.
In recent years, it has become clear that tumor progression and metastases formation is adequately dependent on angiogenesis. Angiogenesis is now recognized as an important control point in cancer therapy. As a result, the microvascular endothelial cell, recruited by a tumor, has become an important second target in cancer therapy. Microvascular endothelial cells, unlike the tumor cells themselves, do not tend to develop drug resistance. Tumor endothelial cells are drug sensitive for long periods of time and may be treated with cytotoxic agents in an “antiangiogenic schedule”. This schedule involves the administration of chemotherapy in low doses, well below the maximum tolerated dose (MTD), in close intervals for extended periods of time (metronomic dosing). As a result, acute toxicity should be avoided and the drugs may be administered to a longer period, eventually converting cancer to a chronic manageable disease. Although this approach has shown promising results for non-small cell lung cancer, breast and ovarian cancer, even low doses of chemotherapeutic drugs, when given metronomically for long periods of time accumulate in the body and cause damage (Browder et al., Antiangiogenic scheduling of chemotherapy improves efficacy against experimental drug-resistant cancer, Cancer Res 2000; 60: 1878-1886).
The taxane paclitaxel (PTX) is a potent anti-neoplastic agent. Paclitaxel is a clinically well established and highly effective anti-neoplastic medication as monotherapy and in combination therapy used for the treatment of metastatic prostate and breast cancer. The primary mode of action of paclitaxel is to promote microtubulin assembly and stabilize them, preventing their depolymerization and thereby inhibiting microtubule dynamics which causes impaired mitosis, leading to cell cycle arrest and finally to apoptosis. Despite its strong anticancer activity, paclitaxel is poorly water-soluble and exhibits serious dose-limiting toxicities and hypersensitivity reactions which originate from the formulating vehicle cremophor EL and the absence of selectivity for target tissue (Gelderblom et al., 2001, Eur J Cancer 37 (13), 1950-8; Bhalla, K. N. Oncogene 2003; 22:9075-90861. In recent years, it has become evident that paclitaxel at low doses has antiangiogenic properties (Wang, et al. Anticancer Drugs 2003; 14: 13-19).
The antiangiogenic schedule of low doses of paclitaxel administered metronomically have been tested on breast cancer patients, and showed promising results with reduced toxicity [Munoz et al., breast, 14:466-79 (2005)]. However, even low doses of paclitaxel, given metronomically, caused side effects.
There are currently eight approved anti-cancer therapies with recognized antiangiogenic properties. These agents, which interrupt critical cell signaling pathways involved in tumor angiogenesis and growth, can be divided into two primary categories: (1) monoclonal antibodies directed against specific proangiogenic factors and/or their receptors; (Avastin, Erbitux, Vectibix, Herceptin) and (2) small molecule tyrosine kinase inhibitors (TKIs) of multiple proangiogenic growth factor receptors (Tarveca, Nexavar, Sutent). Inhibitors of mTOR (mammalian target of rapamycin) represent a third, smaller category of antiangiogenic therapies with one currently approved agent (Torisel). In addition, at least two other approved angiogenic agents may indirectly inhibit angiogenesis through mechanisms that are not completely understood (Velcade, Celgene)
The first FDA-approved angiogenesis inhibitor, Bevacizumab (Avastin, Genentech) a monoclonal antibody to vascular endothelial growth factor (VEGF), has recently been approved for metastatic colon cancer treatment in conjunction with standard conventional chemotherapy.
The largest class of drugs that block angiogenesis are the multi-targeted tyrosine kinase inhibitors (TKIs) that target the VEGF receptor (VEGFR). These drugs such as sunitinib (Sutent, Pfizer), Sorafenib (Nexavar, Bayer/Onyx Pharmaceuticals) and Erlotinib (Tarveca, Gennentech/OSI/Roche) have the advantages of hitting multiple targets, convenient oral administration, and cost effectiveness. While these drugs exhibit promising efficacy, their use is limited by their lack of target specificity, which leads to unexpected toxicity [Cabebe et al. Curr Treat Options Oncol 2007; 8:15-27].
Water-soluble copolymers such as hydroxypropyl methacrylate (HPMA) are biocompatible, non-immunogenic and non-toxic carriers that enable specific delivery into tumor tissue (Satchi-Fainaro et al. Nat Med 2004; 10:255-261). These macromolecules do not diffuse through normal blood vessels but rather accumulate selectively in the tumor site because of the enhanced permeability and retention (EPR) effect. This phenomenon of passive diffusion through the hyperpermeable neovasculature and localization in the tumor interstitium is observed in many solid tumors for macromolecular agents and lipids. Furthermore, conjugation to copolymers, such as HPMA, should restrict the passage through the blood brain bather and would prolong the circulating half-life of the drugs, hence inhibiting the growth of tumor endothelial and epithelial cells by exposing the cells to the conjugated drugs in the circulation for a longer time compared to the free drugs.
An example of the favorable characteristics obtained by conjugation of an anti-angiogenesis agent to HPMA has been described by Satchi-Fainaro et al. in WO 03/086382. This patent application teaches conjugates of water-soluble polymers and the anti-angiogenesis agent TNP-470, and their use as anti-tumor agents, in particular their use as carriers of TNP-470 into tumor vessels, and their effect on the neurotoxicity of TNP-470. According to the teachings of WO 03/086382, an exemplary such conjugate, HPMA-(TNP-470) conjugate (caplostatin), exhibited superior antitumor activity together with a reduced level of toxicity, as compared with TNP-470 alone. WO 03/086382 further suggests incorporation of a targeting ligand, such as RGD (SEQ ID NO:1) or antibodies.
The use of HPMA-TNP-470 conjugate for the treatment of angiogenesis related conditions has also been described in WO 03/086178.
Another example of the increased activity yet reduced toxicity obtained by conjugation of anti-tumor drugs to water-soluble polymers is presented in U.S. Pat. No. 6,884,817.
A HPMA copolymer conjugate of paclitaxel has also been described by Meerum Terwogt et al. [PNU166945; Anticancer drugs 2001; 12:315-323]. This conjugate was aimed at improving drug solubility and providing controlled release of paclitaxel
Bisphosphonates, such as alendronate, are molecules used to treat osteoporosis, bone metastases and to prevent bone fractures. These compounds exhibit an exceptionally high affinity to the bone-mineral hydroxyapatite, and therefore are known to be used also as a targeting moiety (Uludag, H. Curr Pharm Des 2002; 8: 1929-1944).
Alendronate is considered potent for the treatment of bone related diseases and cancer-associated hypercalcemia. It was shown to have antitumor effect in several in vivo cancer models through several different mechanisms [Tuomela et al. 2008, BMC Cancer 8:81; Molinuevo et al. 2007, Eur J Pharmacol 562:28-33; Hashimoto et al. 2005, Cancer Res 65: 540-545]. In addition, alendronate was found to have anti-angiogenic activity through (i) suppression of VEGF-induced Rho activation in an ovarian cancer model [Hashimoto et al. 2007, Biochem Biphys Res Commun 354: 478-484], (ii) inhibition of farnesyl pyrophosphate synthase, in the mevalonate pathway [Russell R G 2007, Pediatrics 119 Suppl 2: S150-162]; and (iii) regulation of cellular level of MMP-2 expression in osteosarcoma cell lines [Cheng et al. 2004, Pediatr Blood Cancer 42; 410-415].
WO 2004/062588 teaches water soluble polymeric conjugate for bone targeted drug delivery with improved pharmacokinetics parameters and better water solubility of the loaded drugs. The polymeric drug delivery systems taught by this application are based on hydroxypropyl methacrylate (HPMA) conjugates of bone-targeting drugs such as alendronate and D-Asp8 (SEQ ID NO: 2) together with a bone-related therapeutic agent (e.g., tetracycline).
PK2 (FCE28069) is a HPMA copolymer-doxorubicin-galactosamine conjugate, which was designed as a treatment for hepatocellular carcinoma or secondary liver disease [Seymour et al. Journal of Clinical Oncology 2002; 20: 1668-1676]. Doxorubicin is an anthracycline antibiotic with limited solubility in physiological fluids, and is a well established anti-neoplastic drug. Galactosamine binds to the hepatic asialoglycoprotein receptor (ASGPR) thus serving as a specific hepatic targeting moiety. These components are linked to the HPMA polymer via an enzymatically biodegradable linker which permits the release of free doxorubicin within the liver, thus increasing the drug concentration in its site of action. The enzymatic degradable linker is a tetrapeptide spacer (Gly-Phe-Leu-Gly; SEQ ID NO: 3), designed for cleavage by lysosomal cathepsins.
O'hare et al. [Journal of Drug Targeting 1993; 1:217-229] have synthesized HPMA copolymers containing doxorubicin and melanocyte stimulating hormone (MSH) as a melanoma specific targeting moiety. Both the doxorubicin and the melanocyte stimulating hormone were linked to the HPMA polymer via an enzymatically biodegradable linker.
Hruby et al. [Journal of Applied Polymer Science 2006; 101:3192-3201] have prepared and synthesized novel polymeric drug-delivery systems designed for bone targeting of anti-neoplastics based on biocompatible HPMA copolymers containing hydroxybisphosphonate targeting moieties and the model drugs radiotherapeutics 125I, imaging agent 111In, or the anticancer drug Doxorubicin.